Commit 7c9e5276 authored by Paolo Bonzini's avatar Paolo Bonzini

scsi, file-posix: add support for persistent reservation management

It is a common requirement for virtual machine to send persistent
reservations, but this currently requires either running QEMU with
CAP_SYS_RAWIO, or using out-of-tree patches that let an unprivileged
QEMU bypass Linux's filter on SG_IO commands.

As an alternative mechanism, the next patches will introduce a
privileged helper to run persistent reservation commands without
expanding QEMU's attack surface unnecessarily.

The helper is invoked through a "pr-manager" QOM object, to which
file-posix.c passes SG_IO requests for PERSISTENT RESERVE OUT and
PERSISTENT RESERVE IN commands.  For example:

  $ qemu-system-x86_64
      -device virtio-scsi \
      -object pr-manager-helper,id=helper0,path=/var/run/qemu-pr-helper.sock
      -drive if=none,id=hd,driver=raw,file.filename=/dev/sdb,file.pr-manager=helper0
      -device scsi-block,drive=hd

or:

  $ qemu-system-x86_64
      -device virtio-scsi \
      -object pr-manager-helper,id=helper0,path=/var/run/qemu-pr-helper.sock
      -blockdev node-name=hd,driver=raw,file.driver=host_device,file.filename=/dev/sdb,file.pr-manager=helper0
      -device scsi-block,drive=hd

Multiple pr-manager implementations are conceivable and possible, though
only one is implemented right now.  For example, a pr-manager could:

- talk directly to the multipath daemon from a privileged QEMU
  (i.e. QEMU links to libmpathpersist); this makes reservation work
  properly with multipath, but still requires CAP_SYS_RAWIO

- use the Linux IOC_PR_* ioctls (they require CAP_SYS_ADMIN though)

- more interestingly, implement reservations directly in QEMU
  through file system locks or a shared database (e.g. sqlite)
Signed-off-by: 's avatarPaolo Bonzini <pbonzini@redhat.com>
parent 092aa2fc
......@@ -171,6 +171,7 @@ trace-events-subdirs += qapi
trace-events-subdirs += accel/tcg
trace-events-subdirs += accel/kvm
trace-events-subdirs += nbd
trace-events-subdirs += scsi
trace-events-files = $(SRC_PATH)/trace-events $(trace-events-subdirs:%=$(SRC_PATH)/%/trace-events)
......
......@@ -33,6 +33,9 @@
#include "block/raw-aio.h"
#include "qapi/qmp/qstring.h"
#include "scsi/pr-manager.h"
#include "scsi/constants.h"
#if defined(__APPLE__) && (__MACH__)
#include <paths.h>
#include <sys/param.h>
......@@ -155,6 +158,8 @@ typedef struct BDRVRawState {
bool page_cache_inconsistent:1;
bool has_fallocate;
bool needs_alignment;
PRManager *pr_mgr;
} BDRVRawState;
typedef struct BDRVRawReopenState {
......@@ -402,6 +407,11 @@ static QemuOptsList raw_runtime_opts = {
.type = QEMU_OPT_STRING,
.help = "file locking mode (on/off/auto, default: auto)",
},
{
.name = "pr-manager",
.type = QEMU_OPT_STRING,
.help = "id of persistent reservation manager object (default: none)",
},
{ /* end of list */ }
},
};
......@@ -413,6 +423,7 @@ static int raw_open_common(BlockDriverState *bs, QDict *options,
QemuOpts *opts;
Error *local_err = NULL;
const char *filename = NULL;
const char *str;
BlockdevAioOptions aio, aio_default;
int fd, ret;
struct stat st;
......@@ -476,6 +487,16 @@ static int raw_open_common(BlockDriverState *bs, QDict *options,
abort();
}
str = qemu_opt_get(opts, "pr-manager");
if (str) {
s->pr_mgr = pr_manager_lookup(str, &local_err);
if (local_err) {
error_propagate(errp, local_err);
ret = -EINVAL;
goto fail;
}
}
s->open_flags = open_flags;
raw_parse_flags(bdrv_flags, &s->open_flags);
......@@ -2597,6 +2618,15 @@ static BlockAIOCB *hdev_aio_ioctl(BlockDriverState *bs,
if (fd_open(bs) < 0)
return NULL;
if (req == SG_IO && s->pr_mgr) {
struct sg_io_hdr *io_hdr = buf;
if (io_hdr->cmdp[0] == PERSISTENT_RESERVE_OUT ||
io_hdr->cmdp[0] == PERSISTENT_RESERVE_IN) {
return pr_manager_execute(s->pr_mgr, bdrv_get_aio_context(bs),
s->fd, io_hdr, cb, opaque);
}
}
acb = g_new(RawPosixAIOData, 1);
acb->bs = bs;
acb->aio_type = QEMU_AIO_IOCTL;
......
======================================
Persistent reservation managers
======================================
SCSI persistent Reservations allow restricting access to block devices
to specific initiators in a shared storage setup. When implementing
clustering of virtual machines, it is a common requirement for virtual
machines to send persistent reservation SCSI commands. However,
the operating system restricts sending these commands to unprivileged
programs because incorrect usage can disrupt regular operation of the
storage fabric.
For this reason, QEMU's SCSI passthrough devices, ``scsi-block``
and ``scsi-generic`` (both are only available on Linux) can delegate
implementation of persistent reservations to a separate object,
the "persistent reservation manager". Only PERSISTENT RESERVE OUT and
PERSISTENT RESERVE IN commands are passed to the persistent reservation
manager object; other commands are processed by QEMU as usual.
-----------------------------------------
Defining a persistent reservation manager
-----------------------------------------
A persistent reservation manager is an instance of a subclass of the
"pr-manager" QOM class.
Right now only one subclass is defined, ``pr-manager-helper``, which
forwards the commands to an external privileged helper program
over Unix sockets. The helper program only allows sending persistent
reservation commands to devices for which QEMU has a file descriptor,
so that QEMU will not be able to effect persistent reservations
unless it has access to both the socket and the device.
``pr-manager-helper`` has a single string property, ``path``, which
accepts the path to the helper program's Unix socket. For example,
the following command line defines a ``pr-manager-helper`` object and
attaches it to a SCSI passthrough device::
$ qemu-system-x86_64
-device virtio-scsi \
-object pr-manager-helper,id=helper0,path=/var/run/qemu-pr-helper.sock
-drive if=none,id=hd,driver=raw,file.filename=/dev/sdb,file.pr-manager=helper0
-device scsi-block,drive=hd
Alternatively, using ``-blockdev``::
$ qemu-system-x86_64
-device virtio-scsi \
-object pr-manager-helper,id=helper0,path=/var/run/qemu-pr-helper.sock
-blockdev node-name=hd,driver=raw,file.driver=host_device,file.filename=/dev/sdb,file.pr-manager=helper0
-device scsi-block,drive=hd
#ifndef PR_MANAGER_H
#define PR_MANAGER_H
#include "qom/object.h"
#include "qapi/qmp/qdict.h"
#include "qapi/visitor.h"
#include "qom/object_interfaces.h"
#include "block/aio.h"
#define TYPE_PR_MANAGER "pr-manager"
#define PR_MANAGER_CLASS(klass) \
OBJECT_CLASS_CHECK(PRManagerClass, (klass), TYPE_PR_MANAGER)
#define PR_MANAGER_GET_CLASS(obj) \
OBJECT_GET_CLASS(PRManagerClass, (obj), TYPE_PR_MANAGER)
#define PR_MANAGER(obj) \
OBJECT_CHECK(PRManager, (obj), TYPE_PR_MANAGER)
struct sg_io_hdr;
typedef struct PRManager {
/* <private> */
Object parent;
} PRManager;
/**
* PRManagerClass:
* @parent_class: the base class
* @run: callback invoked in thread pool context
*/
typedef struct PRManagerClass {
/* <private> */
ObjectClass parent_class;
/* <public> */
int (*run)(PRManager *pr_mgr, int fd, struct sg_io_hdr *hdr);
} PRManagerClass;
BlockAIOCB *pr_manager_execute(PRManager *pr_mgr,
AioContext *ctx, int fd,
struct sg_io_hdr *hdr,
BlockCompletionFunc *complete,
void *opaque);
#ifdef CONFIG_LINUX
PRManager *pr_manager_lookup(const char *id, Error **errp);
#else
static inline PRManager *pr_manager_lookup(const char *id, Error **errp)
{
/* The classes do not exist at all! */
error_setg(errp, "No persistent reservation manager with id '%s'", id);
return NULL;
}
#endif
#endif
......@@ -2241,6 +2241,9 @@
# Driver specific block device options for the file backend.
#
# @filename: path to the image file
# @pr-manager: the id for the object that will handle persistent reservations
# for this device (default: none, forward the commands via SG_IO;
# since 2.11)
# @aio: AIO backend (default: threads) (since: 2.8)
# @locking: whether to enable file locking. If set to 'auto', only enable
# when Open File Descriptor (OFD) locking API is available
......@@ -2250,6 +2253,7 @@
##
{ 'struct': 'BlockdevOptionsFile',
'data': { 'filename': 'str',
'*pr-manager': 'str',
'*locking': 'OnOffAuto',
'*aio': 'BlockdevAioOptions' } }
......
block-obj-y += utils.o
block-obj-$(CONFIG_LINUX) += pr-manager.o
/*
* Persistent reservation manager abstract class
*
* Copyright (c) 2017 Red Hat, Inc.
*
* Author: Paolo Bonzini <pbonzini@redhat.com>
*
* This code is licensed under the LGPL.
*
*/
#include "qemu/osdep.h"
#include <scsi/sg.h>
#include "qapi/error.h"
#include "block/aio.h"
#include "block/thread-pool.h"
#include "scsi/pr-manager.h"
#include "trace.h"
typedef struct PRManagerData {
PRManager *pr_mgr;
struct sg_io_hdr *hdr;
int fd;
} PRManagerData;
static int pr_manager_worker(void *opaque)
{
PRManagerData *data = opaque;
PRManager *pr_mgr = data->pr_mgr;
PRManagerClass *pr_mgr_class =
PR_MANAGER_GET_CLASS(pr_mgr);
struct sg_io_hdr *hdr = data->hdr;
int fd = data->fd;
int r;
g_free(data);
trace_pr_manager_run(fd, hdr->cmdp[0], hdr->cmdp[1]);
/* The reference was taken in pr_manager_execute. */
r = pr_mgr_class->run(pr_mgr, fd, hdr);
object_unref(OBJECT(pr_mgr));
return r;
}
BlockAIOCB *pr_manager_execute(PRManager *pr_mgr,
AioContext *ctx, int fd,
struct sg_io_hdr *hdr,
BlockCompletionFunc *complete,
void *opaque)
{
PRManagerData *data = g_new(PRManagerData, 1);
ThreadPool *pool = aio_get_thread_pool(ctx);
trace_pr_manager_execute(fd, hdr->cmdp[0], hdr->cmdp[1], opaque);
data->pr_mgr = pr_mgr;
data->fd = fd;
data->hdr = hdr;
/* The matching object_unref is in pr_manager_worker. */
object_ref(OBJECT(pr_mgr));
return thread_pool_submit_aio(pool, pr_manager_worker,
data, complete, opaque);
}
static const TypeInfo pr_manager_info = {
.parent = TYPE_OBJECT,
.name = TYPE_PR_MANAGER,
.class_size = sizeof(PRManagerClass),
.abstract = true,
.interfaces = (InterfaceInfo[]) {
{ TYPE_USER_CREATABLE },
{ }
}
};
PRManager *pr_manager_lookup(const char *id, Error **errp)
{
Object *obj;
PRManager *pr_mgr;
obj = object_resolve_path_component(object_get_objects_root(), id);
if (!obj) {
error_setg(errp, "No persistent reservation manager with id '%s'", id);
return NULL;
}
pr_mgr = (PRManager *)
object_dynamic_cast(obj,
TYPE_PR_MANAGER);
if (!pr_mgr) {
error_setg(errp,
"Object with id '%s' is not a persistent reservation manager",
id);
return NULL;
}
return pr_mgr;
}
static void
pr_manager_register_types(void)
{
type_register_static(&pr_manager_info);
}
type_init(pr_manager_register_types);
# scsi/pr-manager.c
pr_manager_execute(int fd, int cmd, int sa, void *opaque) "fd=%d cmd=0x%02x service action=0x%02x opaque=%p"
pr_manager_run(int fd, int cmd, int sa) "fd=%d cmd=0x%02x service action=0x%02x"
......@@ -2893,7 +2893,8 @@ static int machine_set_property(void *opaque,
*/
static bool object_create_initial(const char *type)
{
if (g_str_equal(type, "rng-egd")) {
if (g_str_equal(type, "rng-egd") ||
g_str_has_prefix(type, "pr-manager-")) {
return false;
}
......
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